Granulating devices are known for producing granulates of thermoplastic material by means of rotatable cutting tools which cut strands of material discharged from a die plate. Generally, the cutting of the plastic strands is carried out under water. The die plate is fixed to a granulating head connected to an extruder of the plastic material, the material passing from the extruder through the granulating head to nozzles or orifices in the die plate from which the strands of material are discharged and cut by the cutting tool.
Also known are means for grinding the cutting surfaces of the cutting tools of said granulating devices so that the cutting surfaces are disposed in a common plane parallel to the surface of the die plate from which the strands of plastic material are discharged.
DE-GM 1 918 439 discloses such a grinding means in which the tool head of the cutting blades is maintained stationary and a rotating grinding wheel grinds each cutting blade individually. Thereby, an accurate coplanar, parallel relation of the cutting surfaces of the blades relative to the surface of the die plate is not initially achieved by this arrangement. Therefore, in order to achieve the desired coplanar, parallel relation of the cutting surfaces of the blades with the surface of the die plate, the cutting head is applied with slight pressure against the surface of the die plate.
In this way, the cutting surfaces of the cutting tools are collectively brought into precise planar parallel relation with the surface of the die plate and deviations in the rotating cutting tool head caused by given tolerances are equilibrated. This is necessary in order to obtain a satisfactory shearing of the molten, plastic strands discharged from the outlets of the nozzles in the dip plate.
Additionally, a new adjustment of individual cutting tools is required after they have been replaced and this is conducted, in the same way, for equilibration with the die plate. This, so-called "cutting-in" operation, however is very time consuming and requires a shutdown of granulate production which may last for several hours.
It is also known that ideal conditions for granulating plastics and similar materials are obtained during the cutting process only if all the cutting tools are applied with their entire bearing surfaces at a uniform prestress, adapted to the properties of the product, against the entire front surface of the die plate swept by the cutting tools.
The conventional means of arranging the front surface of the die plate and the cutting surface of the cutting tools strictly parallel and coplanar to one another and of pressing the cutting tools with defined force against the die plate are not sufficient to obtain a planar, parallel relation of the cutting tools under identical prestress at the die plate.
In addition to the time-consuming effort in the known "cutting-in" process, a process and a device are disclosed in the unpublished German Patent Application P 4,221,776, which allows the cutting tool head to rotate at a predetermined angular velocity in order to simultaneously cut all cutting surfaces of the cutting tools by a fine adjustment against a grinding wheel or plate. As a result, the planar, parallel relation of the cutting tools relative to the surface of the die plate necessarily involves high precision for the fine adjustment of the cutting tools against the grinding wheel. For this purpose, a complex system and a considerable financial expenditure is necessary.